Exemplary embodiments of the invention relate to a welding tool for connecting at least two workpieces at a connection region by means of friction stir welding.
In friction stir welding, in contrast to friction welding, the friction energy is not generated by rotation of one of the two workpieces being connected relative to the other workpiece; rather, a wear-resistant welding tool applies rotational energy to the two workpieces. In the process, the following steps are carried out:
In the first step, the welding tool and the rotating probe thereof are pressed with high force into a connection region between the two workpieces being connected, until a shoulder of the welding tool, the shoulder surrounding the probe in a contactless manner, comes to rest on the surface of the workpieces.
In the second step, the rotating probe remains on the welding start point for a brief time, and the connection region between the shoulder of the welding tool and the workpieces heats up to just below the melting point of the material of the workpieces. In this process, the workpieces become soft and plasticize, such that a mixing of the materials of the workpieces being connected is possible in the connection region.
In the third step, the welding tool is moved in the direction of advancement in such a manner that the probe and the shoulder continue to be pressed against the surface of the workpieces with high force. During the advancement movement, a pressure difference is created between the forward region of the welding tool and the rearward end thereof, as a result of the rotary movement of the probe, such that plasticized material is transported around the probe, mixes, and therefore contributes to the formation of the welded seam.
At the end of the welded seam, the welding tool is removed from the connection region.
The welding tool therefore comprises the probe and the shoulder, the same having a larger diameter than the probe itself and being arranged substantially perpendicularly thereto. The shoulder serves the purpose of insulating the welded seam from the surrounding air, while the probe is responsible for the stirring of the material. Because the material is utilized to form the welded seam, by means of the stirring, no additional materials are required. In addition, there is no need to use an inert gas atmosphere.
The friction stir welding process has the disadvantage that the shoulder must be in continuous contact with the workpieces being welded, and as a result, the freedom of movement of the welding tool in three dimensions is restricted. By way of example, it is not possible to weld containers all the way into the corners thereof, it is not possible to weld scarf joints and flange seams, and excesses of material are created that must be removed by further treatment.
Exemplary embodiments of the invention are directed to a welding tool that can be used to overcome the problems named above.
A welding tool for connecting at least two workpieces at a connection region by means of friction stir welding has a shoulder for the purpose of separating the connection region from the surroundings. The shoulder is designed as a molding tool.
As such, it is possible to adapt the shoulder to the respective welding situation, and it is possible to produce connections which have previously not been possible using friction stir welding. This is because the accessibility of the probe to the connection region being welded is improved by means of the adapted shoulder.
The shoulder is preferably designed and constructed for the purpose of molding the connection region.
The connection region is preferably the specific region of the at least two workpieces that is heated by the friction energy during the friction stir welding process. This means that it is preferably not only the plasticized joining zone, but also a region adjacent thereto, which is heated at least to the extent that it can be molded or deformed.
The shoulder preferably has a projection on and/or next to a shoulder surface that is intended to be arranged on the connection region during the friction stir welding. As such, it is possible, by way of example, to place the projection on one side of an edge of the workpiece, while the shoulder surface is positioned on the other side of the edge of the workpiece. According to the design of the region between the shoulder surface and the projection, the edge of the workpiece can be molded at the same time, and, for example, a rounding, a bevel, and/or a chamfer can be formed.
The projection is also preferably given a stepped design on a projection surface that is intended to be arranged on the connection region during the friction stir welding process. As such, it is also possible to tightly press the workpieces being connected together, for example in the direction of advancement, by means of the stepped profile of the projection surface, and therefore to join the metal together by a flange, for example.
The steps of the projection surface in this case can be connected to each other perpendicularly or via a slope, or via a rounding, by way of example.
Multiple projections are advantageously formed on and/or next to the shoulder surface. As such, a multi-faceted molding is also possible, in an advantageous manner, in the connection region of two workpieces being connected.
In one particularly preferred embodiment, the projection is designed for the purpose of molding a bevel and/or a rounding and/or a chamfer on the connection region, particularly on an edge of the connection region. In this case, the projection surface, together with the shoulder surface, has a negative counter-shape to the bevel and/or the rounding and/or the chamfer, by way of example, which is then guided in the direction of advancement along the workpieces being connected, in the connection region. As an advantageous result, there is no need to treat the final workpiece formed as a result of the connection of the two workpieces.
In a further advantageous manner, the shoulder has a shoulder surface region with a convex and/or concave curve. As such, it is advantageously also possible to weld together two workpieces with small convex and/or concave radii, in a simple manner.
In a particularly preferred manner, the shoulder is designed for the purpose of molding the connection region and/or the at least one workpiece. Due to the applied friction energy, the workpiece material softens and can then be molded. For this reason, it is possible to form fluid transitions between the two workpieces being connected, in a simple manner, by means of the shoulder pressed on the connection surface, the shoulder being designed as a molding tool, without the need to use additional material.
It is further advantageous that the shoulder is designed for the purpose of molding a welded seam created during the friction stir welding process at the connection region. As such, it is possible to dispense with a subsequent treatment of the welded seam.
A welding method for connecting at least two workpieces at a connection region by means of friction stir welding has the following steps:                a) provision of the described welding tool;        b) friction stir welding at the connection region with simultaneous molding of the connection region and/or of the at least one workpiece and/or a welded seam formed as a result.        
It is particularly preferred that a workpiece is produced by means of the described welding tool and/or by means of the described welding method.